REVIEW FOR CHAPTER 6 – VOLCANOES Where can we find volcanoes on earth? Most volcanoes are found near subduction zones and mid-ocean ridges. This explains why the map of volcanoes on Earth matches so well the map of tectonic plates. On the other hand, some volcanoes are located in remote places like in the middle of the Pacific plate (Hawaii), thousands of kilometres away from the nearest plate boundary. Before lava reaches the surface, the molten material is called? magma Main hazards from a quiet volcanic eruption is…. Lava flow Sometimes rising magma is blocked by horizontal layers of rock. The magma forces the layer of rock to bend upward into a landform called Dome Mountain Chapter 6 Volcanoes Landforms From Lava and Ash • Composite Volcanoes have quiet eruptions that alternate with explosive eruptions, forming layers of lava and ash. Chapter 6 Volcanoes Stages of Volcanic Activity • Extinct volcanoes are considered “dead” meaning that it is unlikely that they will erupt again Chapter 6 Volcanoes Stages of Volcanic Activity • Dormant volcanoes are considered “asleep” or “sleeping bears” meaning that they may become active in the future Chapter 6 Volcanoes Stages of Volcanic Activity • Active volcanoes are considered “live” meaning that it is erupting, or has shown signs that it may erupt in the near future Chapter 6 Volcanoes Magma Reaches Earth’s Surface • Pyroclastic flow is an explosive eruption that includes hot gases, cinders (volcanic ash), and bombs (volcanic rocks). Chapter 6 Volcanoes Magma Reaches Earth’s Surface • Aa is a very thick, slow moving lava. Aa contains high amounts of silica, which gives it it’s thickness. When aa hardens, it forms a rough surface consisting of jagged (sharp) lava chunks. Chapter 6 Volcanoes Magma Reaches Earth’s Surface • Pahoehoe is a very thin, fast moving lava. Pahoehoe contains low amounts of silica, which gives it it’s thinness. When Pahoehoe hardens, it forms wrinkle and rope-like rock formations. Pahoehoe is hotter than Aa. Chapter 6 Volcanoes Magma Reaches Earth’s Surface • When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. Chapter 6 Volcanoes Landforms From Magma • Sills Chapter 6 Volcanoes Landforms From Magma • Dikes Chapter 6 Volcanoes Landforms From Magma • Volcanic Necks Chapter 6 Volcanoes Landforms From Magma • Batholiths Chapter 6 Volcanoes Landforms From Lava and Ash • Calderas are formed when a magma chamber is emptied after an eruption and the volcano mountain collapses into the empty space creating a crater. Crater Lake, Oregon Chapter 6 Volcanoes Landforms From Lava and Ash • Lava Plateaus are formed from runny lava (pahoehoe) that cools in flat sheets of rock. Over time these layers form high plateaus. Steamboat Rock, Washington Chapter 6 Volcanoes Landforms From Lava and Ash • Cinder Cone Volcanoes have explosive eruptions of ash, cinders, and bombs that form a cone-shaped hill. Mount Etna, Italy Chapter 6 Volcanoes Landforms From Lava and Ash • Shield Volcanoes have quiet eruptions and have gentle slopes, which are not steep.